The present invention is related in general to digital communication systems, and more particularly to a method and system for selecting a communications parameter for communicating with a concentrated subscriber unit having multiple subscriber terminals sharing a transceiver.
In many communications systems, transceivers in an infrastructure system are designed to communicate with subscriber units distributed throughout a communications system service area. One example of such a communications system is a wireless cellular communications system, wherein the cellular infrastructure system provides communication services to subscriber units in various locations throughout the cellular system coverage area.
In some communications systems, selected subscriber units may be fixed in a particular location, rather than mobile and free to move about the coverage area. When a subscriber unit is fixed, and several subscriber units are used in the vicinity of that same location, an opportunity arises for subscriber units to share communications resources, such as sharing a transceiver in a wireless communications system.
With reference now to FIG. 1, there is depicted a communications system 20 wherein subscriber units 22-26 communicate with infrastructure 28. Infrastructure 28 may be coupled to the public switched telephone network (PSTN) 30 so that subscriber units 22-26 may communicate with others connected to PSTN 30. Within infrastructure 28, base station controller 32 may be coupled to base stations 34 and 36, wherein base station controller 32 provides base stations 34 and 36 with control and traffic data. If communications system 20 is a cellular communication system, supporting mobile subscriber units, base station controller 32 may be used to route communication traffic to a selected base station for serving each particular subscriber unit.
As shown at subscriber unit 26, some subscriber units may be xe2x80x9cconcentrated subscriber unitsxe2x80x9d that support multiple subscriber terminals 38. A subscriber terminal may be thought of as a communications interface to communications system 20. For example, if concentrated subscriber unit 26 is a fixed wireless terminal, terminals 38 within concentrated subscriber unit 26 may provide a local loop telephone system interface for coupling to a telephone handset, such as telephone 40. Note that if telephones 40 are in the same vicinity, such as in the same building, subscriber terminals 38 may all share transceiver 46 in order to communicate with base station 36. Thus, in a concentrated subscriber unit, S number of subscriber terminals 38 may share transceiver resources provided by T number of transceivers, wherein S is greater than T. This sharing of transceiver resources reduces the cost and complexity of concentrated subscriber unit 26.
When communications system 20 grows to support a larger number of subscriber units, the communications system will need to add additional capacity to service those subscribers. Capacity may be added by increasing the number of transmission frequencies, or otherwise increasing the number of channels available to subscribers, wherein such channels and frequencies are used in various ways known in the art to separate data intended for one subscriber from another subscriber. In the example of communications system 20, base stations 34 and 36 each transmit on two carrier frequencies, illustrated at first carrier 42 and second carrier 44.
For the most part, subscriber terminals 38 appear to infrastructure 28 as separate subscriber units that can be tuned to separate frequencies and set to separate channels, like subscriber units 22 and 24. However, a problem exist with concentrated subscriber unit 26 when transceiver 46 is supporting subscriber terminals 38 that have been instructed to tune to different frequencies, such as first and second carriers 42 and 44. The problem occurs because transceiver 46 is typically designed to receive and transmit on a single carrier frequency. Thus, concentrated subscriber unit 26 works better when subscriber terminals 38 are instructed, as group, to select the same communication parameter, such as the same carrier frequency. By operating subscriber terminals 38 as a group, the benefits of sharing a transceiver 46 are maximized.
In communications system 20, subscriber units 22-26 and infrastructure 28 may agree upon a formula for selecting communications parameters, such as carrier frequency or other channel designation parameters. This formula for selecting communications parameters is used to reduce the number of messages transferred between infrastructure 28 and subscriber units 22-26, and to randomly distribute the selection of communication parameters so that capacity of the system is increased, and the success of accessing the communications system is increased. This random distribution attempts to spread subscriber units evenly among the carrier frequencies, for example.
In the prior art, communication parameters are selected by performing a hashing function on an identification number associated with the subscriber unit or subscriber terminal. For example, to select one of two carrier frequencies, both infrastructure 28 and subscriber unit 22 will input an ID number associated with subscriber unit 22 into a hashing function that hashes the ID number to produce a number indicating one of the two carrier frequencies that is being used to communicate between infrastructure 28 and subscriber unit 22. If four carrier frequencies are available, the hashing function outputs an indicator having one of four values so that one of four carrier frequencies may be selected.
Typically, the subscriber unit identification number is based on the telephone number associated with the subscriber unit. In concentrated subscriber unit 26, it is desirable to have a different phone number for each terminal unit 38. Furthermore, it may be desirable to have sequential phone numbers assigned to terminal units 38. The problem occurs in the prior art when the ID numbers for terminal units 38 hash, as a group, to more than one carrier frequency, or more carrier frequencies than transceiver 46 can support.
One solution to this problem, is described in U.S. Pat. No. 5,544,223, which shows a communications system that includes a database for recording which subscriber units are concentrated subscriber unit and which subscriber units are not. The disadvantages of this system include transmitting additional messages to indicate that a subscriber unit is a concentrated subscriber unit, and the recording, in a database, the subscriber unit status. This system requires additional overhead in messaging and data storage.
Thus, it should be apparent that a need exist for an improved method and system for selecting a communication parameter, such as a carrier frequency, for communicating with a concentrated subscriber unit in a communication system, wherein the number of overhead messages is reduced and a database indicating a concentrated subscriber unit is not required.
Thus there is a particular need for a method and system for selecting a communication parameter, such as a carrier frequency, for communicating with a concentrated subscriber unit in a communication system, wherein the number of overhead messages is reduced and a database indicating a concentrated subscriber unit is not required. Briefly, in accordance with an embodiment of the present invention, a subscriber terminal identification number in one of multiple subscriber terminals is determined. Next, N number of selected digits in the subscriber terminal identification number are set equal to predetermined values to produce a modified subscriber terminal identification number. The modified subscriber terminal identification number is then hashed using a hashing function to produce a communication parameter indicator. The communication parameter is selected in response to the communication parameter indicator, wherein groups of subscriber terminal identification numbers having non-selected digits with the same value are hashed to produce the same communication parameter indicator.